Throughout this application, various publications, patents, and published patent applications are referred to by an identifying citation. The disclosures of the publications, patents, and published patent specifications referenced in this application are hereby incorporated by reference into the present disclosure to more fully describe the state of the art to which this invention pertains.
As the evolution of batteries continues, and particularly as lithium batteries become more widely accepted for a variety of uses, the need for safe, long lasting high energy batteries becomes more important. There has been considerable interest in recent years in developing high energy density cathode-active materials for use in high energy primary and secondary batteries with lithium containing anodes. Various types of cathode materials for the manufacture of lithium batteries are known in the art.
One class of lithium batteries known in the art are rechargeable lithium batteries where the battery is able to undergo multiple discharge and recharge cycles. During discharge of a lithium cell, lithium ions are formed and extracted from the anode and inserted into the cathode. On recharge, the reverse process occurs. The electrodes used in these batteries can have a dramatic effect on the performance of the battery and, in particular, on cycle life.
Another class of lithium batteries known in the art are primary lithium batteries. A primary battery differs from a rechargeable battery in that it is only designed to be discharged once. In fact, because of the design, attempts to recharge a primary battery may create safety problems and may be only partially effective for a very limited number of cycles. Examples of lithium primary cells are described by Nishio et al. in Handbook of Battery Materials, Chapter 2, “Practical Batteries”, pp. 31-40, Elsevier, Amsterdam, (1999) and by Linden in Handbook of Batteries, Chapter 14, pp. 5-6, McGraw-Hill, New York (1995). Primary, non-rechargeable cells, with their single discharge, have a short lifetime and their disposal burden is high, which makes the choice of the cathode material and its impact on the environment of great importance. Sulfur is an attractive cathode-active material for primary cells, both from an environmental perspective and from its very high theoretical specific capacity of 1675 mAh/g in the lithium-sulfur couple.
U.S. Pat. No. 4,410,609 to Peled et al. describes a primary cell comprising an anode consisting of lithium or a dischargeable alloy of lithium, an electrolyte comprising a solvent to dissolve both an electrolyte salt and polysulfides at a low concentration, and an inert porous cathode current collector, which may be loaded with sulfur. Yamin et al., in Electrochemical Society Proceedings, 1984, Volume 84-1, 301-310, describe low rate lithium/sulfur batteries in which the primary cells have a porous carbon cathode current collector impregnated with sulfur and in which the cell's electrolyte is a lithium polysulfide saturated solution of 1M LiClO4 in tetrahydrofuran-toluene mixtures. The room temperature energy density for these cells is reported to be 730 Wh/Kg.
In a study of dioxolane-based solvents for lithium-sulfur batteries, Peled et al., in J. Electrochem. Soc., 1989, 136, 1621-1625, report that dioxolane-rich solvents are compatible with lithium but that sulfur utilization is only 50% due to the final reduction (discharge) product, Li2S2.
There is a need to enhance the performance of primary and rechargeable lithium electrochemical cells. In studies on lithium/thionyl chloride cells, performance enhancement has been achieved by the addition of halide additives. For example, Linden, in Handbook of Batteries, Chapter 14, pp. 44-47, McGraw-Hill, New York (1995), summarizes data showing an increase in cell voltage and energy density by the addition of BrCl to lithium/thionyl chloride cells. In U.S. Pat. Nos. 4,784,925 and 4,784,927 to Klinedinst et al., small quantities of iodine or iodine monochloride are reported to act as catalysts to increase output voltage and output capacity of lithium/thionyl chloride cells.
Sodium-sulfur cells, which typically operate at high temperatures, such as 300° C. to 350° C., also typically operate at a capacity less than theoretical to avoid precipitation of insoluble Na2S and Na2S2. U.S. Pat. No. 4,018,969 to Fisher et al., and U.S. Pat. Nos. 4,184,013, 4,216,276, and 4,238,553 to Weddigen et al. describe additives which increase the solubility of Na2S and Na2S2 in the liquid sulfur cathode and thereby increase the capacity of high temperature sodium-sulfur cells.
Despite the various approaches proposed for the fabrication of lithium cells, there remains a need for higher energy density and-safer and more environmentally acceptable primary and rechargeable lithium cells.
It is, therefore, an object of the present invention to provide lithium cells which have higher energy density.
It is another object of the present invention to provide cells which are safe and which comprise environmentally acceptable materials.